From 122ae1ee27275588ba5912f8d8d882df2b986347 Mon Sep 17 00:00:00 2001
From: engrbm87 <engrbm87@gmail.com>
Date: Sun, 6 Jan 2019 20:26:42 +0200
Subject: [PATCH] fix empty prefix issue

When switchtopic is set to a different topic the prefix will be empty so its length will be zero. In the Shorten function the strncmp will give a zero result because the prefixlen is zero and will add '~' even though there is no prefix.
Adding prefixlen != 0 in the if condition fixes the issue. Also skip adding the prefix "~" on line 292 by checking if the prefix length is greater than zero.
---
 sonoff/xdrv_12_home_assistant.ino | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sonoff/xdrv_12_home_assistant.ino b/sonoff/xdrv_12_home_assistant.ino
index 26609d1d7..59a7b519e 100644
--- a/sonoff/xdrv_12_home_assistant.ino
+++ b/sonoff/xdrv_12_home_assistant.ino
@@ -147,7 +147,7 @@ static void Shorten(char** s, char *prefix)
 {
   size_t len = strlen(*s);
   size_t prefixlen = strlen(prefix);
-  if (len > prefixlen && !strncmp(*s, prefix, prefixlen)) {
+  if (len > prefixlen && prefixlen != 0 && !strncmp(*s, prefix, prefixlen)) {
     *s += prefixlen-1;
     *s[0] = '~';
   }
@@ -289,7 +289,7 @@ void HAssAnnounceButtonSwitch(byte device, char* topic, byte present, byte key,
     snprintf_P(mqtt_data, sizeof(mqtt_data), HASS_DISCOVER_DEVICE_INFO, mqtt_data,
                unique_id, ESP.getChipId(),
                Settings.friendlyname[0], ModuleName().c_str(), my_version, my_image, "Tasmota");
-    snprintf_P(mqtt_data, sizeof(mqtt_data), HASS_DISCOVER_TOPIC_PREFIX, mqtt_data, prefix);
+    if (strlen(prefix) > 0 ) snprintf_P(mqtt_data, sizeof(mqtt_data), HASS_DISCOVER_TOPIC_PREFIX, mqtt_data, prefix);
     snprintf_P(mqtt_data, sizeof(mqtt_data), PSTR("%s}"), mqtt_data);
   }
   MqttPublish(stopic, true);